In traditional semiconductor manufacturing field, forming strained source/drain regions in semiconductor devices has become a significant mean for improving performance of semiconductor devices by generating compressive stress or tensile stress onto channels, which accordingly enhances carriers mobility inside channels. Specific processes for manufacturing said semiconductor devices are described here below in conjunction with FIG. 1(a): providing a bulk Si substrate 100 that has a gate stack; firstly, etching the bulk Si substrate 100 on both sides of the gate stack to form trenches; then filling, for example Boron doped SiGe or Phosphorus/Arsenic doped Si:C into the trenches to form strained source/drain regions 110.
However, since leakage current that occurs between source/drain regions 110 and the bulk Si substrate 100 may deteriorate performance of semiconductor devices, bulk Si substrates have been replaced by Silicon-On-Insulator (SOI) in the prior art for reducing leakage current between substrates and source/drain regions. As shown in FIG. 1(b), the SOI substrate 100′ comprises a base layer 101, an insulating layer 102 and an active layer 103. Embedded source/drain regions 110 are formed in the active layer 103 of the SOI substrate 100′. Due to presence of the insulating layer 102, the source/drain regions 110 are separated from the base layer 101, which effectively eliminates pathway for leakage current (with reference to areas enclosed by dotted lines in FIG. 1(a) and FIG. 1(b)) and accordingly suppresses leakage current between the substrate 100′ and the source/drain regions 110. Nonetheless, since the active layer 103 of the SOI substrate is usually thin, the source/drain regions 110 formed thereon do not extend deeply due to thickness of the active layer 103. Consequently, contact resistance at the source/drain regions 110 may increase, and performance of semiconductor devices may deteriorate.
Accordingly, it is needed to solve such problems as how to reduce contact resistance at source/drain regions while suppressing leakage current between substrate and source/drain regions.